We might put the question slightly differently: What scientific problems require knowledge of the global variability of lower atmospheric electric generators? In this paper, we present our view of the necessity of quantifying global electrical variability and discuss some potential uses of and available methods for producing a geoelectric index.
During this last decade, we have observed an increasing interest in the field of atmospheric electricity. At the 1985 AGU Fall Meeting in San Francisco, Calif., there were seven half-day sessions on various aspects of atmospheric electricity—a great increase over past years (see the abstract listings for the Atmospheric Sciences and SPR: Magnetospheric Physics sessions in Eos, November 12, 1985, pp. 815–842 and 1028–1055). This area of interest covers thunderstorm electrification, lightning, and sferics, as well as lightning-induced magnetospheric effects and solar-terrestrial electromagnetic coupling. For many aspects of these studies, it would be advantageous to have a number that is a measure of present global electrical activity, such as thunderstorm occurrence, number of lightning events, or ionospheric electric potential relative to the earth [see also Markson and Muir, 1980]. Furthermore, there are many other areas of research that would benefit from a geoelectric index, such as meteorology and atmospheric science.